Recently, a large amount of sealed documents such as direct mail, debit notes and the like are conveyed or mailed from various enterprises to customers by mail and the like, and various automatic mail enclosing and sealing machines have thus been utilized. In such machines, the content of each envelope has been checked automatically.
In a typical prior art mail enclosing and sealing machine, the content of the enclosures being enclosed is checked by measuring the thickness and/or the weight of the enclosure, comparing the measured thickness and/or the weight with a predetermined value.
However, such a machine cannot be utilized when the number and/or the size of the enclosures being enclosed in respective envelopes is not fixed.
Further, prior art thickness and/or weight detecting devices are not satisfactory in terms of reliability and applicability.